The present invention relates to centrifugal pumps in general, and, more in particular, to centrifugal pumps of the pitot tube type and to improvements in the pitot tube geometry of such pumps.
Pitot tube type centrifugal pumps are known. An illustrative description of such a pump can be found in U.S. Pat. No. 3,384,024 to King.
In general, the pumps have a rotor driven in rotation by a prime mover. The rotor houses a stationary pitot tube. The pitot tube extends radially in a cavity in the rotor and has a passage for passing fluid. The pitot tube has an entrance for receiving fluid proximate the outer radial boundary of the rotor cavity. This fluid has received an energy input from the prime mover through the rotor. Typically, some of the velocity head of the fluid in the pitot tube is changed to pressure head through a diffuser.
Pitot tube pumps are relatively efficient and have good pressure and flow rate characteristics. It is obviously desirable to have these pumps as efficient as possible. Fluid losses occasioned through boundary layer separation in the pitot tube is an area of concern. Another area of concern is pitot tube drag.
The pitot tube defines a flow passage which is circumferential at its entrance, turns to become radial and then turns again to become axial of the rotor. These two turns are about 90.degree., the first being slightly greater. Clearly separation of fluid from the walls as the fluid traverses these turns adds to flow loss. The possibility of avoiding substantial flow losses in bends by increasing the flow cross-sectional area on the inside of the bend is discussed in NASA Tech Brief 68-10395 by Gerlach.